Nitrate Concentration in Greenland Ice: an Indicator of Changes in Fluxes of Solar and Galactic High-Energy Particles

Abstract

Two sets of nitrate (NO3−) concentration data in Central Greenland ice, obtained through the GISP2 collaboration and by the University of Kansas, were analyzed statistically. The two records correlate well over time scales from a few years up to a century. They both contain quasi five-year, decadal and century-type time variations. A quasi five-year periodicity resulting from increases in the mean nitrate concentration before and after maximum sunspot number was confirmed. A tendency of solar proton events to occur more frequently during the rise/decline phases of the solar cycle may cause a quasi five-year variation. Century-type (60–110 yr) variability in nitrate outstrips the corresponding Gleissberg cycle in sunspots by 12–17 years and changes synchronously (correlates with zero phase shift) with the smoothed length of the solar Schwabe cycle. A significant correlation between century-type periodicities for nitrates in Greenland ice and northern Fennoscandian temperatures was established. The results show that despite a strong dependence on local meteorology, nitrate concentration in ice contains valuable information about global geophysical phenomena in the past.